Inhuman Desire 'stacks' by modifying v1, rather than giving multiple instances.Only instance of a stackable perk I can think of is Inhuman Desires...
What are you looking at to determine if it stacks?So Breed Hungry will stack with itself if you edit in multiple but on a save/reload the extras are removed.
To my knowledge, weight isn't factored into applying penalties, only size.The belly/ball weight reduction, which can effectively 0 it out, but too much of a pain in ass to resetting every session.